Process for controlling a rotating machine, a servocontrol system for implementing said method and a rotating machine provided with a system of this kind

ABSTRACT

In a process for controlling a rotating machine having n phases powered by a voltage inverter defining m n  states of the stator phase voltage vector the electromagnetic torque Γ and the stator flux |φ s  | of the machine are servocontrolled. A calculator calculates a succession of n states of the phase voltage vector to move the torque Γ and the flux |φ s  | towards the set points Γ ref , |φ s  | ref . On each sampling, the calculator calculates the remaining application time of the current state and the updated application times of the future states of the phase vector. Asynchronously with the sampling times and the calculation times, the calculator sends SPmLL switch control signals to switch from the current state to the next state.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a processor controlling a rotating machine, aservocontrol system for implementing said method and a rotating machineprovided with a system of this kind.

To be more precise, the invention concerns a method of controlling theelectromagnetic torque and the stator flux of an asynchronous rotatingmachine having a high dynamic range from low speeds to high speeds.

2. Description of the Prior Art

U.S. Pat. No. 4,678,248 concerns a control method in which the controlparameters are the electromagnetic torque and the stator flux.

The method uses vector modeling of the machine and of the voltageinverter.

The electromagnetic torque of the machine is known to be a function ofthe angle between the rotor flux rotating vector and the stator fluxrotating vector and the moduli of these flux vectors. In other words,the electromagnetic torque Γem is a function of the vector product ofthe rotating flux vectors:

    Γ.sub.em =K (φ.sub.R ×φ.sub.s)

The stator voltage vector V_(s) is delivered by a three-phase voltageinverter, each phase including a two-state SP2LL (Single Pole 2 LogicLevels) switch. Accordingly, the stator voltage vector V_(s) can assumeeight states V₁ . . . V₈ (2³), of which two V₁, V₈ are of null amplitude(null states) in the stator fixed frame of reference (α, β), accordingto the combination of the three SP2LL switches of the inverter.

The DTC (Direct Torque Control) system relies on maintaining the modulus|φ_(s) | of the stator flux rotating vector φ_(s) in a hysteresis band Hin the stator frame of reference (α, β) and on controlling the torqueΓ_(em) by accelerating the stator flux rotating vector φ_(s) relative tothe rotor flux φ_(R) to increase the torque Γ_(em) (increase the anglebetween the two flux vectors) and by stopping the stator flux vectorφ_(x) so that the rotor flux vector φ_(R) catches up with it to reducethe torque Γ_(em) (reducing the angle between the two flux vectors).

The stator flux vector φ_(s) is controlled by means of a finite table.This table contains, for a given location N_(i) (i=1 . . . 6) of thestator flux vector φ_(s) rotating in the plane in the stator (α, β), thestates V₁ . . . V₈ of the stator phase voltage vector V_(s) which enablethe stator flux vector to be stopped (null states V₁, V₈) and those foropening the angle between the flux vectors φ_(s), φ_(R) whilstmaintaining the stator flux vector φ_(s) in the hysteresis band H.

In the case of low rotor rotation speeds, the response dynamic of theabove solution is very poor. In particular, the negative step responsetime is in the order of four times the response time of a positive stepof the same amplitude.

Furthermore, the proposed technique dedicates control of the stator flux(maintenance of the stator flux modulus in the hysteresis band) totorque control. Configurations in which stator flux control is requiredconcomitantly with control of the torque Γ_(em) are not provided for.

U.S. Pat. No. 5,610,485 concerns an asynchronous rotating machinecontrol method using the DTC method for one range of speeds and addinghysteresis to the torque. Moreover, the method provides two additionalmodes of operation, one for low speeds and the other for high speeds.

The mode of operation at low speeds is based on the imposition of aninverter switching frequency.

The mode of operation at high speeds is the full wave mode.

One of the major disadvantages of the above methods results from thefact that switching from one phase vector state to another phase vectorstate is effected at sampling times when the control system registersovershooting of one of the hystereses. Accordingly, for the system tohave a good dynamic (to prevent an excessive overshoot) it is necessaryto use very short sampling periods (T_(ech) =50 μs; f_(ech) =20 kHz)leading to high sampling frequencies that are significantly higher thanthe sampling frequencies generally used in real time devices.

Furthermore, the problem of stator flux control (maintaining the statorflux modulus in the hysteresis band) dedicated to torque control has notbe solved. Configurations in which stator flux control is requiredconcomitantly with control of the torque Γ_(em) are still not providedfor.

Finally, the change to full wave mode is not simple to effect.

One aim of the present invention is to propose a method of controllingthe electromagnetic torque and the stator flux of an asynchronousrotating machine in which the inverter switching times are predicted bycalculation and carried out asynchronously with the sampling orcalculation times. In this way the sampling frequencies no longer needto be as high as in the prior art and are reduced to the frequenciesused as standard in prior art real time devices (between 2 kHz and 5kHz).

Another aim of the present invention is to propose a method ofcontrolling the electromagnetic torque and the stator flux of anasynchronous rotating machine in which the electromagnetic torque andthe stator flux can be regulated concomitantly.

Another aim of the present invention is to propose a method ofcontrolling the electromagnetic torque and the stator flux of anasynchronous rotating machine in which the change to full wave mode doesnot require any change of strategy.

SUMMARY OF THE INVENTION

To this end the invention concerns a process for controlling a rotatingmachine with n phases supplied with alternating current by a voltageinverter comprising n SPmLL switches defining m^(n) states of the statorphase voltage vector, the electromagnetic torque Γ and the stator flux|φ_(s) | of said machine being slaved to set points Γ_(ref), |φ_(s)|_(ref) by a servocontrol system that can employ various controlstrategies, each strategy having application conditions, saidservocontrol system including a set of sensors the values sensed bywhich are transmitted to an observer-sampler, the outputs of theobserver, sampled at a given sampling period T_(e), being fed into acalculator, said calculator outputting control signals for the SPmLLswitches of the voltage inverter.

In this process, and in accordance with the application conditions ofthe control strategy employed, the calculator calculates a succession ofn states of the phase voltage vector to move the torque Γ and the flux|φ_(s) | towards the set points Γ_(ref), |φ_(s) |_(ref) by successivelyswitching n states of the succession and the application time dt_(k) k ε{1, . . . ,n} of each of said n states of the succession, on eachsampling, the calculator calculates the remaining application time ofthe current state and the updated application times of the future statesof the phase vector, and asynchronously with the sampling times and thecalculation times, at the end of the application time of the currentstate, the calculator sends SPmLL switch control signals to switch fromthe current state to the next state.

In one mode of operation, the calculator performing the calculations inan orthogonal three-dimensional calculation frame of referencecomprising the stator plane (φ_(s)α, φ_(s)β) of the stator flux φ_(s)and an axis perpendicular to said stator plane (φ_(s)α, φ_(s)β)representing the torque Γ, the set points Γ_(ref), |φ_(s) |_(ref) beingrepresented by a circle η_(ref) contained in a plane parallel to thestator plane (φ_(s)α, φ_(s)β), centered on said perpendicular axis,having a radius |φ_(s) |_(ref) and intercepting said perpendicular axisat Γ_(ref), the values Γ, φ_(s) supplied by the rotating machine beingrepresented by a point A (φ_(s)α, φ_(s)β, Γ) on a circle η contained ina plane parallel to the stator plane (φ_(s)α, φ_(s)β), centered on saidperpendicular axis, having a radius |φ_(s) | and intercepting saidperpendicular axis at Γ, the control strategy is a strategy asynchronouswith the rotation frequency of the rotating machine in which thesuccession of n states of the voltage vector is calculated so that thepoint A (φ_(s)α, φ_(s)β, Γ) converges to any point D of a circleη_(cal), centered on said perpendicular axis, having a radius |φ_(s)|_(cal) and intercepting said perpendicular axis at Γ_(cal) bysuccessive application of the n states, in a predetermined given time,said calculator calculating the equation of the circle η_(cal) so thatthe application time of the succession, the mean torque Γ and the meanstator flux |φ_(s) | generated are respectively substantially equal tothe set points Γ_(ref), |φ_(s) |_(ref).

In particular, n being equal to three, the control strategy is based onthe application of a SOCMLI cycle such that the calculator looks for aunique triplet of states (V₀, V_(i), V_(adj)) iε{2 . . . m^(n) -1} ofthe voltage vector constituting a succession of three states comprisingan initial state V_(i), one of the two states V_(adj) adjacent to V_(i)and a null state (V₀), the respective application times dt_(i),dt_(adj), dt₀ of which are positive and such that their sum is equal tohalf the switching period T_(d) of the inverter.

Accordingly, the process steps are:

a) the calculator looks for the unique triplet (V₀, V_(i), V_(adj)) iε{2. . . m^(n) -1} and calculates the presumed arrival point D' on thecircle η_(cal),

b) it sends the SPmLL switch control signals to switch to the stateV_(i),

c) on each sampling, the calculator calculates for the current point A'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(ir) of application ofthe state V_(i) and the updated times dt_(adj) and dt₀ of the futurestates V_(adj) and V₀,

d) if dt_(ir) ≦T_(e) the calculator predicts the switching time from thestate V_(i) to the state V_(adj),

e) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to the state V_(adj),

f) on each sampling, the calculator calculates for the current point B'(φ_(s)αc, φ_(s)βc, Γ_(c) ) the remaining time dt_(adjr) of applicationof the state V_(adj) and the updated time dt₀ of the future state V₀,

g) if dt_(adjr) ≦T_(e) the calculator predicts the switching time fromthe state V_(adj) to the state V₀,

h) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to the state V₀,

i) on each sampling, the calculator calculates for the current point C'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application ofthe state V₀,

j) if dt_(0r) ≦T_(e), the calculator looks for a new unique triplet(V'₀, V'_(i), V'_(adj)) iε{2 . . . m^(n) -1} and predicts the switchingtime from the state V₀ to the state V'_(i),

k) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL controlsignals to switch to the state V'_(i),

the calculator processing the new triplet (V'₀, V'_(i), V'_(adj)) byapplying steps c) through k).

In step c) the calculator solves the following system: ##EQU1## where λis a parameter defining the position of the point D on a tangent to thecircle η_(cal) at D'.

In step f) the calculator solves the following system using the leastsquares method: ##EQU2##

In step i) the calculator calculates for the current point C' (φ_(s)αc,φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application of the stateV₀ by using the least squares method to solve the following system:##EQU3##

In step d) the calculator predicts the switching from the state V_(i) tothe other state adjacent V_(i) in order to re-align the trajectory ofthe point B' towards the circle η_(cal).

If there is no unique triplet (V₀, V_(i), V_(adj)) the calculator looksfor a succession of two states (V_(i), V_(adj)) other than a null statefor the best approximation to the point A (φ_(s)α, φ_(s)β, Γ) on thecircle η_(ref) in the time interval 1/2T_(d).

In another mode of operation, the calculator performing the calculationsin an orthogonal three-dimensional calculation frame of referencecomprising the stator plane (φ_(s)α, φ_(s)β) of the stator flux φ_(s)and an axis perpendicular to said stator plane (φ_(s)α, φ_(s)β)representing the torque Γ, the set points Γ_(ref), |φ_(s) |_(ref) beingrepresented by a circle η_(ref) contained in a plane parallel to thestator plane (φ_(s)α, φ_(s)β), centered on said perpendicular axis,having a radius |φ_(s) |_(ref) and intercepting said perpendicular axisat Γ_(ref), the values Γ, φ_(s) supplied by the rotating machine beingrepresented by a point A (φ_(s)α, φ_(s)β, Γ) on a circle η contained ina plane parallel to the stator plane (φ_(s)α, φ_(s)β), centered on saidperpendicular axis, having a radius |φ_(s) | and intercepting saidperpendicular axis at Γ, the control strategy is a strategy synchronouswith the rotation frequency of the rotating machine in which thesuccession of n states of the voltage vector is calculated so that thepoint A (φ_(s)α, φ_(s)β, Γ) converges to a point D on a circle η_(cal)centered on said perpendicular axis, having a radius |φ_(s) |_(cal) andintercepting said perpendicular axis at Γ_(cal), by successiveapplication of the n states, with a predetermined final position of thestator flux vector in the stator plane (φ_(s)α, φ_(s)β), said calculatorcalculating the equation of the circle η_(cal) so that the applicationtime of the succession, the mean torque Γ and the mean stator flux|φ_(s) | generated are respectively substantially equal to the setpoints Γ_(ref), |φ_(s) |_(ref).

The number of predetermined positions authorized for each rotation ofthe stator flux is finite and dependent on a range of rotation speed ofthe rotating machine.

In particular, n being equal to three, the control strategy is such thatthe calculator knows a unique triplet of states (V₀, V_(i), V_(adj))iε{2 . . . m^(n) -1} of the voltage vector constituting a succession ofthree states, comprising an initial state V_(i), one of the two statesV_(adj) adjacent to V_(i) and a null state (V₀), the respectiveapplication times dt_(i), dt_(adj), dt₀ of which are positive, saidtriplet intercepting the circle η_(cal) at a known point D.

Accordingly, in a rotary machine initialization step, triplets (V₀,V_(i), V_(adj)) iε{2 . . . m^(n) -1} are stored in memory in thecalculator for going from one predetermined position to anotherpredetermined position of the stator flux vector, according to variousrotating machine rotation speed ranges, and, in operation,

a) the calculator knows the triplet (V₀, V_(i), V_(adj)) to be appliedaccording to the rotation speed of the rotating machine and thepredetermined position at which the stator flux vector is located,

b) it sends the SPmLL switch control signals to switch to state V_(i),

c) on each sampling, the calculator calculates for the current point A'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(ir) of application ofthe state V_(i) and the updated times dt_(adj) and dt₀ of the futurestates V_(adj) and V₀,

d) if dt_(ir) ≦T_(e) the calculator predicts the time of switching fromthe state V_(i) to the state V_(adj),

e) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to state V_(adj),

f) on each sampling the calculator calculates for the current point B'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(adjr) of application ofthe state V_(adj) and the updated time dt₀ of the future state V₀,

g) if dt_(adjr) ≦T_(e) the calculator predicts the time of switchingfrom the state V_(adj) to the state V₀,

h) asynchronously with the sampling times and the calculation times,when the switching time arrives the calculator sends the SPmLL switchcontrol signals to switch to the state V₀,

i) on each sampling the calculator calculates for the current point C'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application ofthe state V₀,

j) if dt_(0r) ≦T_(e) the calculator predicts the time of switching fromthe state V₀ to the state V'_(i) and additionally the calculator knowsthe new unique triple (V'₀, V'_(i), V'_(adj)) for going from thepredetermined position that is about to be reached to the nextpredetermined position of the stator flux vector, and

k) asynchronously with the sampling times and the calculation times,when the switching time arrives the calculator sends the SPmLL switchcontrol signals to switch to the state V'_(i),

the calculator processing the new triplet (V'₀, V'_(i), V'_(adj)) inaccordance with steps c) through k.

In step c) the calculator solves the following system: ##EQU4##

In step f) the calculator solves the following system: ##EQU5## where λis a parameter defining the predictable final position of the currentpoint B' on a straight line in the stator plane passing through thetorque Γ axis and parallel to the predetermined position of the statorflux vector to be reached.

In step i) the calculator calculates for the current point C' (φ_(s)αc,φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application of the stateV₀ by solving the following system: ##EQU6## where Γ_(mean) is the meanelectromagnetic torque calculated over the time interval dt_(i)+dt_(adj).

The change to full wave mode results from the fact that the time dt₀ ofapplication of the null state is a decreasing function of the rotationspeed of the rotating machine and equal to zero beyond a predeterminedvalue of the rotation speed of the rotating machine.

The invention also consists in a servocontrol system for implementingthe method described hereinabove.

The invention finally concerns a rotating machine provided with aservocontrol system of the above kind.

A first advantage of the present invention results fromdesynchronization of the switching times from the calculation times andthe sampling times, which allows a significant increase in the samplingperiod and therefore application of the process with standard samplingdevices.

Another advantage of the present invention results from the fact of theexplicit presence of the concept of time which makes it possible to takeinto account in a reliable manner the switching frequency and minimumconduction time constraints inherent to power converters.

Another advantage of the present invention is an optimal torque dynamiceven at low speeds.

Other advantages and features of the present invention will result fromthe following description with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a device in accordance with theinvention.

FIGS. 2 and 3 are schematic illustrations of a calculation example inthe asynchronous mode of the invention.

FIGS. 4 and 5 are schematic illustrations of a calculation example inthe synchronous mode of the invention.

FIG. 6 is a schematic representation of a full wave mode correctionexample in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention concerns a method of controlling a rotating machine 1 withn phases supplied with alternating current by a voltage inverter 3comprising n (SPmLL: Single Pole m Logic Levels) switches 4 with mpositions defining m^(n) states V_(i) iε{1, . . . ,m^(n) } of the statorvoltage phase vector V_(s).

The electromagnetic torque Γ and the stator flux |φ_(s) | of the machine1 are slaved to set points Γ_(ref), |φ_(s) |_(ref) by a servocontrolsystem 5 that can use various control strategies, each strategy havingapplication conditions.

The servocontrol system 5 includes a set of sensors 7, 8, 9 the valuessensed by which are transmitted to an observer-sampler 10.

The outputs of the observer 10, sampled at a given sampling periodT_(e), are fed into a calculator 13.

The calculator 13 outputs control signals 6 for the SPmLL switches 4 ofthe voltage inverter 3.

The outputs of the observer 10 are representative values of the torque Γand the stator flux |φ_(s) |.

In addition to the sampled outputs, the calculator also receives asinput the representative values of the set points Γ_(ref) and |φ_(s)|_(ref).

The invention is more particularly concerned with the steps of theprocess that execute in the calculator 13.

In accordance with the application conditions of the control strategyemployed, the calculator 13 calculates a succession of n states of thephase voltage vector V_(s) to move the torque Γ and the flux |φ_(s) |towards the set points Γ_(ref), |φ_(s) |_(ref) by successively switchingn states of the succession and the application time dt_(k) k ε {1, . . .,n} of each of the n states of the succession.

On each sampling, the calculator calculates the remaining applicationtime of the current state and the updated application times of thefuture states of the phase vector.

Asynchronously with the sampling and the calculation times, at the endof the application time of the current state, the calculator sends SPmLLswitch 4 control signals to switch from the current state to the nextstate.

The process described hereinabove therefore enables the future switchingtimes to be predicated by calculation and switching to be performed atthe calculated times independently of the sampling times or thecalculation times.

In the embodiment described, although this is not limiting on theinvention, the calculator advantageously performs the calculations in anorthogonal three-dimensional calculation frame of reference comprisingthe stator plane (φ_(s)α, φ_(s)β) of the stator flux φ_(s) and an axisperpendicular to the stator plane (φ_(s)α, φ_(s)β) representing thetorque Γ.

In this calculation space, the set points Γ_(ref), |φ_(s) |_(ref) arerepresented by a circle η_(ref) contained in a plane parallel to thestator plane (φ_(s)α, φ_(s)β) centered on the perpendicular axis havinga radius |φ_(s) |_(ref) and intercepting said perpendicular axis atΓ_(ref).

Similarly, the current values Γ, φ_(s) supplied by the rotating machineare represented by a point A (φ_(s)α, φ_(s)β, Γ) on a circle η containedin a plane parallel to the stator plane (φ_(s)α, φ_(s)β), centered onsaid perpendicular axis with a radius |φ_(s) | and intercepting saidperpendicular axis at Γ_(c).

Finally, the control strategies of the process are strategies in whichthe succession of n states of the voltage vector is calculated so thatthe point A (φ_(s)α, φ_(s)β, Γ) converges to any point D on a circleη_(cal) centered on said perpendicular axis having a radius |φ_(s)|_(cal) and intercepting said perpendicular axis at Γ_(cal) bysuccessive application of the n states.

To this end the calculator calculates the equation of the circle η_(cal)so that for the duration of application of the succession of n statesthe mean torque Γ and the mean stator flux |φ_(s) | generated arerespectively substantially equal to the set points Γ_(ref), |φ_(s)|_(ref).

In the embodiment described, in order to simplify the illustration ofthe process, the rotating machine is a three-phase machine and theinverter includes SP2LL switches. The process can nevertheless beapplied to a machine with n phases and SPmLL switches.

Thus in the embodiment described there are eight possible states (V₁, .. . ,V₈) of the phase vector V_(s), two of which are of zero amplitude(V₁, V₈). The process therefore applies a triplet of states to movetowards the set points.

Provided that it exists, the process preferably applies a triplet (V₀,V_(i), V_(adj)) iε{2 . . . m^(n) -1} made up of a succession of threestates comprising an initial state V_(i), one of the two states V_(adj)adjacent to V_(i) and a null state V₀.

The process must therefore define the respective application timesdt_(i), dt_(adj), dt₀ of the triplet. Adjustment of these threedurations authorizes three degrees of freedom. Control such that at theend of application of the triplet the torque and the stator flux must beon η_(cal) constrains only two degrees of freedom. An additionalconstraint must therefore be applied in order to be able to determinethe three application times.

The process of the invention proposes two additional constraints eachdetermining a different control strategy:

A asynchronous control strategy whereby the additional constraint is aconstraint of time to be respected at the end of application of thetriplet, independent of the position of the stator flux rotating vector.

A synchronous control strategy whereby the additional constraint is aconstraint imposing a position of the stator flux rotating vector at theend of application of the triplet independently of the time elapsed forapplication of the triplet.

In the asynchronous strategy (FIGS. 2, 3):

the control strategy is based on application of a cycle such that thecalculator looks for a unique triplet of states (V₀, V_(i), V_(adj))iε{2 . . . m^(n) -1} of the voltage vector constituting a succession ofthree states comprising an initial state V_(i), one of the two statesV_(adj) adjacent to V_(i) and a null state V₀, the respectiveapplication times of which dt_(i), dt_(adj), dt₀ are positive and suchthat their sum is equal to half the switching period T_(d) of theinverter:

    dt.sub.i +dt.sub.adj +dt.sub.0 =1/2T.sub.d

The uniqueness of the triplet does not imply that it exists. If thecalculator cannot find a triplet having three positive applicationtimes, the process launches a third control strategy known as the largetransients strategy described below.

In the asynchronous control strategy:

a) the calculator looks for the unique triplet (V₀, V_(i), V_(adj)) iε{2. . . m^(n) -1} and calculates the presumed arrival point D' on thecircle η_(cal),

b) it sends the SPmLL switch control signals to switch to the stateV_(i),

c) on each sampling, the calculator calculates for the current point A'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(ir) of application ofthe state V_(i) and the updated times dt_(adj) and dt₀ of the futurestates V_(adj) and V₀,

d) if dt_(ir) ≦T_(e) the calculator predicts the switching time from thestate V_(i) to the state V_(adj),

e) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to the state V_(adj),

f) on each sampling, the calculator calculates for the current point B'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(adjr) of application ofthe state V_(adj) and the updated time dt₀ of the future state V₀,

g) if dt_(adjr) ≦T_(e) the calculator predicts the switching time fromthe state V_(adj) to the state V₀,

h) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to the state V₀,

i) on each sampling, the calculator calculates for the current point C'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application ofthe state V₀,

j) if dt_(0r) ≦T_(e), the calculator looks for a new unique triplet(V'₀, V'_(i), V'_(adj)) iε{2 . . . m^(n) -1} and predicts the switchingtime from the state V₀ to the state V'_(i),

k) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL controlsignals to switch to the state V'_(i),

the calculator processing the new triplet (V'₀, V'_(i), V'_(adj)) byapplying steps c) through k).

In one example of calculation by the process of the invention (FIGS. 2,3), the state V_(i) is applied to the segment AB. At each sampling time(step c)) the calculator calculates the application times for thecurrent point A' by solving the following system of three equations inthree unknowns: ##EQU7##

The above system of three equations in three unknowns is linearized byreplacing the presumed point of arrival D' with a plane G tangential atD' to the circle η_(cal).

The above system when linearized amounts to solving the followingsystem: ##EQU8## where λ is a parameter defining the position of thepoint D on a tangent to the circle η_(cal) at D' such that ##EQU9##where D is not imposed and where ##EQU10## according to the stateV_(index) of the stator phase vector V_(s).

The reader will understand that in order to calculate the directionalderivatives the model of the rotating machine must have been input tothe calculator beforehand.

(SA1) therefore supplies the three application times dt_(ir), dt_(adj),dt₀ at each sampling time on the segment AB.

When V_(adj) is applied (segment BC), the loss of the degree of freedomtied to V_(i) causes the process to reduce its ambitions as to theaccuracy at the end of the triplet. Solving the system (SA1) with dt_(i)=0 does not provide an exact solution. The calculator adopts anapproximate solution that minimizes the error. The calculator uses theleast squares method, for example.

The calculator uses the least squares method to solve the followingsystem (step f)): ##EQU11##

(SA2) supplies the application times dt_(adjr) and dt₀.

When V₀ is applied (segment CD) the loss of the degree of freedom tiedto Vadj causes the process to reduce its ambitions as to the accuracy atthe end of the triplet.

At the end of application of the triplet there will therefore be adouble inaccuracy (triplet application time and torque value at the endof the triplet). Solving the system (SA2) with dt_(adj) =0 does notprovide an exact solution. The calculator adopts an approximate solutionthat minimizes the error. The calculator uses the least squares method,for example.

The calculator uses the least squares method to solve the followingsystem (step i)):

solving the following system by the least squares method: ##EQU12##

(SA3) calculates dt_(0r).

In step d) the calculator can predict switching from state V_(i) to theother state adjacent V_(i) in order to realign the trajectory of thepoint B' towards the circle η_(ref). This can be necessary if the setpoints are significantly modified during dt_(i). Accordingly, thecalculator can decide that application of the other state adjacent V_(i)is no longer optimal. The other state adjacent V_(i) will then beapplied during the predicted time dt_(adj).

In the FIG. 3 representation the circles η_(cal), η_(ref) have the sameradius. The calculator could determine circles having different radii,however.

If there is no unique triplet (V₀, V_(i), V_(adj)) with positive dt_(i),dt_(adj), dt₀, then the calculator switches to the "large transients"control strategy.

The calculator looks for a succession of two states (V_(i), V_(adj))different from a null state leading to an optimum approximation of thepoint A (φ_(s)α, φ_(s)β, Γ) on the circle η_(ref) in the time period1/2T_(d).

To give just one example, the calculator could look for the pair ofadjacent states minimizing the error:

    ε=χ·ε.sub.φ +(1-χ)·ε.sub.r

This error allows weighted treatment of stator flux and torque errors.

Moreover, the constraint dt_(i) +dt_(adj) =1/2T_(d) guaranteesreasonable ripple on the parameters characteristic of the process.

In the case of the synchronous strategy (FIGS. 4, 5): the succession ofn states of the voltage vector is calculated so that the point A(φ_(s)α, φ_(s)β, Γ) converges to a point D on the circle η_(cal) bysuccessive application of the n states and with a predetermined positionof the stator flux vector in the stator plane (φ_(s)α, φ_(s)β).

The number of predetermined positions authorized per rotation of theflux vector is finite and depends on a range of rotation speeds of therotating machine.

In the case of a three-phase rotating machine and an inverter usingSP2LL switches, the control strategy is such that the calculator knows aunique triplet of states (V₀, V_(i), V_(adj)) iε{2 . . . m^(n) -1} ofthe voltage vector constituting a succession of three states, comprisingan initial state V_(i), one of the two states V_(adj) adjacent V_(i) anda null state (V₀), the respective application times of which dt_(i),dt_(adj), dt₀ are positive, the triplet intercepting the circle η_(cal)at a required point D.

In this process:

in a rotary machine initialization step, triplets (V₀, V_(i), V_(adj))iε{2 . . . m^(n) -1} are stored in memory in the calculator for goingfrom a predetermined position to another predetermined position of thestator flux vector, according to various rotating machine rotation speedranges, and

in operation,

a) the calculator knows the triplet (V₀, V_(i), V_(adj)) to be appliedaccording to the rotation speed of the rotating machine and thepredetermined position at which the stator flux vector is located,

b) it sends the SPmLL switch control signals to switch to the stateV_(i),

c) on each sampling, the calculator calculates for the current point A'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(ir) of application ofthe state V_(i) and the updated times dt_(adj) and dt₀ of the futurestates V_(adj) and V₀,

d) if dt_(ir) ≦T_(e) the calculator predicts the time of switching fromthe state V_(i) to the state V_(adj),

e) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to the state V_(adj),

f) on each sampling, the calculator calculates for the current point B'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(adjr) of application ofthe state V_(adj) and the updated time dt₀ of the future state V₀,

g) if dt_(adjr) ≦T_(e) the calculator predicts the time of switchingfrom the state V_(adj) to the state V₀,

h) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL switchcontrol signals to switch to the state V₀,

i) on each sampling, the calculator calculates for the current point C'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application ofthe state V₀,

j) if dt_(0r) ≦T_(e), the calculator predicts the time of switching fromthe state V₀ to the state V'_(i) and additionally the calculator knowsthe new unique triple (V'₀, V'_(i), V'_(adj)) for going from thepredetermined position that is about to be reached to the nextpredetermined position of the stator flux vector, and

k) asynchronously with the sampling times and the calculation times,when the switching time arrives, the calculator sends the SPmLL controlsignals to switch to the state V'_(i),

the calculator processing the new triplet (V'₀, V'_(i), V'_(adj)) inaccordance with steps c) through k).

In one example of calculation in accordance with the invention (FIGS. 4,5) the state V_(i) is applied to the segment AB. The calculatorcalculates the application times for the current point A' at eachsampling time by solving the following system ##EQU13## where θ is theangle fixed to arrive at the imposed point D.

In step c), the calculator solves the following linear system: ##EQU14##where D is imposed.

(SS1) therefore supplies the three application times dt_(ir), dt_(adj),dt₀ for each sampling time on the segment AB.

When V_(adj) is applied (segment BC), the loss of the degree of freedomtied to V_(i) causes the process to reduce its ambitions as to theaccuracy at the end of the triplet. The objective tied to the amplitudeof the stator flux is abandoned. Accordingly, in step f), the calculatorsolves the following system: ##EQU15## where λ is a parameter definingthe predictable final position of the current point B' on a straightline in the stator plane passing through the torque Γ axis and parallelto the predetermined position of the stator flux vector to be reached.

(SS2) therefore provides the two application times dt_(adjr), dt₀ andthe value of λ for each sampling time on the segment BC.

When V₀ is applied (segment CD), the loss of the degree of freedom tiedto V_(adj) causes the process to reduce its ambitions as to the accuracyat the end of the triplet. Only the torque objective is retained. It iscarefully chosen because the mechanical speed is high. Accordingly, instep i), the calculator calculates the remaining time dt_(0r) forapplication of the state V₀ for the current point C' (φ_(s)αc, φ_(s)βc,Γ_(c)) by solving the following system: ##EQU16## where Γ_(mean) is themean electromagnetic torque calculated over the time interval dt_(i)+dt_(adj).

In the FIG. 5 representation, the circles η_(cal), η_(ref) have the sameradius. The calculator could nevertheless determine circles havingdifferent radii.

The null state application time dt₀ is a decreasing function of therotating machine rotation speed and is equal to zero beyond apredetermined value of the rotating machine rotation speed.

This latter feature makes it a simple matter to change from thesynchronous control strategy to the full wave strategy. In a first stagethe null state application time dt0 tends to zero, and then cancels. Thesystem is then in the full wave mode.

The reader will understand that in the full wave mode the fact that thenull state application time dt₀ is equal to zero means that it is nolonger possible to control the torque directly. The torque of therotating machine is then controlled by way of the flux, in accordancewith the following rules:

To increase the torque Γ angle between the stator flux and the rotorflux is increased. To achieve this the rotation of the stator fluxvector is accelerated. This implies reducing the stator flux norm.

To reduce the torque Γ the angle between the stator flux and the rotorflux is reduced. To achieve this the rotation speed of the stator fluxvector is reduced. This implies increasing the stator flux norm.

This form of control is exercised by an applied stator flux corrector inaccordance with the difference between the instantaneous torque and theset point torque.

The torque is regulated by the flux corrector as a function ofΔΓ=Γ_(ref) -Γ_(c) in accordance with the following rules:

For ΔΓ>0 the corrector decreases the stator flux norm.

For ΔΓ<0 the corrector increases the stator flux norm.

The invention also concerns a servocontrol system for implementing theprocess described hereinabove.

The invention finally concerns a rotating machine provided with aservocontrol system of the above kind.

Of course, the invention is not limited to the embodiment or applicationdescribed, but is susceptible to many variants that will be evident tothe skilled person and do not depart from the scope of the invention. Inparticular, the number of phases, the number of logic levels of eachsingle pole, the calculation space and the calculation systems can bevaried without departing from the scope of the invention.

What is claimed is:
 1. A process for controlling a rotating machineincluding n phases supplied with alternating current by a voltageinverter comprising n SPmLL switches, wherein m comprises a number oflevels represented by a single switch, said n SPmLL switches definingm^(n) states of a stator phase voltage vector, wherein anelectromagnetic torque Γ and a stator flux |φ_(s) | of said rotatingmachine is slaved to set portions Γ_(ref), |φ_(s) |_(ref) by aservocontrol system in accordance with various control strategies, eachstrategy of said various control strategies having applicationconditions, said servocontrol system including a set of sensors whoseoutputs are transmitted to a sampler for sampling at a sampling periodT_(e) to provide sampled values for the electromagnetic torque and thestator flux of said rotating machine, the sampled values being input toa calculator, said calculator outputting control signals for said SPmLLswitches of said voltage inverter in accordance with said applicationconditions of the control strategy employed, said process forcontrolling said rotating machine comprising:successively switching nstates of said phase voltage vector to move said torque Γ and said flux|φ_(s) | towards said set points Γ_(ref), |φ_(s) | in succession inaccordance with an application time where dt_(k) where k ε{1, . . . , n}for applying each of said n states of said succession, said successiveswitching occurring on each sampling, calculating a remainingapplication time of a current state of said phase vector and calculatingand an updated application time of future states of said phase vector,and synchronously with the sampling times and the calculation times,sending SPmLL switch control signals to switch from said current stateto the next state to control the rotating machine at the end of theapplication time of said current state.
 2. The control process claimedin claim 1, wherein said calculator performs calculations in anorthogonal three-dimension calculation frame of reference comprising astator place (φ_(s)α, φ_(s)β) of said stator flux φ_(s) and an axisperpendicular to said stator plane (φ_(s)α, φ_(s)β) representing saidtorque Γ,wherein said set points Γ_(ref), |φ_(s) | are represented by acircle η_(ref) contained in a plane parallel to said stator plane(φ_(s)α, φ_(s)β), centered on said perpendicular axis, having a radius|φ_(s) |_(ref) and intercepting said perpendicular axis at Γ_(ref),wherein the values Γ, φ_(s) supplied by said rotating machine arerepresented by a point A (φ_(s)α, φ_(s)β, Γ) on a circle η contained ina plane parallel to said stater plane A (φ_(s)α, φ_(s)β), centered onsaid perpendicular axis, having a radius φ_(s) | and intercepting saidperpendicular axis at Γ, and wherein said control strategy is a strategyasynchronous with a rotation frequency of said rotating machine, whereinsaid successively switching step further comprises calculating saidsuccession of n states of said voltage vector so that said point A(φ_(s)α, φ_(s)β, Γ) converges to any point D of a circle η_(cal),centered on said perpendicular axis, having a radius |φ_(s) |_(cal) andintercepting said perpendicular axis at Γ_(cal) by successiveapplication of said n states, in a predetermined given time; calculatingthe equation of said circle η_(cal) so that the application times ofsaid succession of phase vector voltages generates a mean torque Γ and amean stator flux that are respectively substantially equal to said setpoints Γ_(ref), |φ_(s) |_(ref).
 3. The control process claimed in claim2 wherein n is equal to three, and said control strategy is based on acycle comprising:searching for a unique triplet of states (V₀, V_(i),V_(adj))iε{2. . . m^(n-) 1} of said m^(n) possible voltage vectorstates, said unique triplet succession constituting a succession ofthree states comprising an initial state V_(i), one of the two statesV_(adj) adjacent to V_(i) and a null state (V₀), and wherein respectiveapplication times dt_(i), dt_(adj), dt₀ of said unique triplet arepositive and such that their sum is equal to half a switching periodT_(d) of said inverter.
 4. The control process claimed in claim 3wherein said step for searching for unique triplet comprises:a)calculating a presumed arrival point D' on said circle η_(cal), b)sending said SPmLL switch control signals to switch to said state V_(i)based on said presumed arrival point, c) on each sampling, calculatingfor a current point A' (φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining timedt_(ir) of application of said state V_(i) and updated times dt_(adj),and dt₀ of the future states V_(adj) and V₀, then d) if dt_(ir) ≦T_(e),predicting the switching time from said state V_(i) to said stateV_(adj), then e) asynchronously with said sampling times and saidcalculation times, when said switching times arrives for switching fromsaid state V_(i) to said state V_(adj), sending said SPmLL switchcontrol signals to switch to said state V_(adj), f) on each sampling,calculating for a current point B' (φ_(s)αc, φ_(s)βc, θ_(c)) a remainingtime dt_(adjr) of application of said state V_(adj) and an updated timedt₀ of said future state V₀, g) if dt_(adjr) ≦T_(e), predicting theswitching time from said state V_(adj) to said state V₀, then h)asynchronously with said sampling times and said calculation times, whensaid switching time arrives for switching from said state V_(adj) tosaid state V₀, sending said SPmLL switch control signals to switch tosaid state V₀, then i) on each sampling, calculating for a current pointC' (φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining time dt_(or) of application ofsaid state V₀, then j) if dt_(0r) ≦T_(e), searching for a new uniquetriplet (V'₀ V'₁, V'_(adj))iε{2. . . m^(n) -1} and predicting aswitching time from said state V₀, to said state V'_(i), then k)asynchronously with said sampling times and said calculation times, whensaid switching times arrives for switching from said state V₀ to saidstate V'i sending said SPmLL control signals to switch to said stateV'_(i), thenprocessing the new unique triplet (V'₀, V'_(i), V'_(adj)) byapplying steps c) through k) respectively for state V'₀, V'_(i) andV'_(adj).
 5. The control process claimed in claim 4 wherein in step c)said calculating step comprises solving the following system todetermine the remaining time dt_(ir1) and updated times dt_(adj) and dt₀: ##EQU17## where λ is a parameter defining the position of said point Don a tangent to said circle η_(cal) at D', and where (1/2)T_(d) -t_(c)is a time remaining before a new period (1/2)T_(d) and in step f) saidcalculating step comprises solving the following system using the leastsquares method to determine the remaining application time dt.sub.αdjand the updated time dt₀ : ##EQU18## where (1/2)T_(d) -t_(c) is a timeremaining before a new period (1/2)T_(d).
 6. The process claimed inclaim 4 wherein in step i), said calculating step comprises solving C'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(or) of application ofstate V₀ by using a least squares method to solve the following system:##EQU19## where (1/2)T_(d) -t_(c) is a time remaining before a newperiod (1/2)T.sub..
 7. The process claimed in claim 4 wherein in step d)said predicting step comprises switching from said state V_(i) toanother state adjacent to V_(i) in order to re-align the trajectory ofsaid point B' towards said circle η_(cal).
 8. The process claimed inclaim 3, wherein if said searching step fails to identify a uniquetriplet (V₀, V_(i), V_(adj)) that satisfies conditions for dt_(i),dt_(adj) and dt₀ and Td, said process comprises searching for asuccession of two states (V_(i), V_(adj)) other than a null state for abest approximation to said point A (φ_(s)α, φ_(s)β, Γ) on said circleη_(ref) in the time interval (1/2)T_(d).
 9. The control process claimedin claim 1, wherein said calculator performs calculations in anorthogonal three-dimensional calculation frame of reference comprising astator plane (φ_(s)α, φ_(s)β) of said stator flux φ_(s) and an axisperpendicular to said stator plane (φ_(s)α, φ_(s)β) representing saidtorque Γ, wherein said set points Γ_(ref), |φ_(s) |_(ref) arerepresented by circle η_(ref) contained in a plane parallel to saidstator plane (φ_(s)α, φ_(s)β), centered on said perpendicular axishaving a radium |φ_(s) |_(ref) and intercepting said perpendicular axisat Γ_(ref), wherein the values Γ, φ_(s) supplied by said rotatingmachine are represented by a point A (φ_(s)α, φ_(s)β, Γ), centered onsaid perpendicular axis, having a radius |φ_(s) | and intercepting saidperpendicular axis at Γ, and wherein said control strategy synchronouswith a rotation frequency of said rotating machine wherein saidsuccessively switching step further comprises calculating saidsuccession of n states of said voltage vector so that said point A(φ_(s)α, φ_(s)β, Γ) converges to a point D on a circle η_(cal) centeredon said perpendicular axis, having a radius |φ_(s) |_(cal) andintercepting said perpendicular axis at Γ_(cal), by successiveapplication of said n states, with a predetermined final position ofsaid stator flux vector in said stator plane (φ_(s)α,φ_(s)β);calculating the equation of said circle η_(cal) so that theapplication times of said succession of said phase vector voltagesgenerates a mean torque Γ and a mean stator flux |φ_(s) | that arerespectively substantially equal to said set points Γ_(ref), |φ_(s)|_(ref).
 10. The control process claimed in claim 9 wherein a number ofpredetermined positions authorized for each rotation of said stator fluxis finite and dependent on a range of rotation speed of said rotatingmachine.
 11. The control process claimed in claim 9 wherein, n is equalto three, and said control strategy is such that a unique triplet ofstates (V₀, V_(i), V_(adj))iε{2. . . m^(n) -1} of said m^(n) possiblevoltage vectors constitutes a succession of three states, comprising aninitial state V_(i), one of the two states V_(adj) adjacent to V_(i) anda null state (V₀), the respective application times dt_(i), dt_(adj),dt₀ of which are positive, said triplet intercepts said circle η_(cal)at a known point D.
 12. The control process claimed in claim 11comprising a rotary machine initialization step, wherein triplets (V₀,V_(i), V_(adj))iε{2. . . m^(n) -1} are stored in memory in saidcalculator for going from one predetermined position to anotherpredetermined position of said stator flux vector, according to variousrotating machine rotation speed ranges, said process furthercomprising:applying a particular triplet (V₀, V_(i), V_(adj)) accordingto the rotation speed of said rotating machine and the predeterminedposition at which said stator flux vector is located, b) sending saidSPmLL switch control signals to switch to state V_(i), c) on eachsampling, calculating for a current point A' (φ_(s)αc, φ_(s)βc, Γ_(c)) aremaining time dt_(ir) of application of said state V_(i) and updatedtimes dt.sub.αdj and dt₀ of said future state V_(adj) and V₀, d) ifdt_(ir) ≦T_(e) predicting the time of switching from said state V_(i) tostate V_(adj), e) asynchronously with said sampling times and saidcalculation times, when said switching time arrives to switch from stateV_(i) to state V_(adj), sending said SPmLL switch control signals toswitch to state V_(adj), f) on each sampling, calculating for a currentpoint B' (φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining time dt_(adjr) ofapplication of said state V_(adj) and an updated time dt₀ of said futurestate V₀, g) if dt_(adjr) ≦T_(e), predicting the time of switching fromsaid state V_(adj) to said state V₀, h) asynchronously with saidsampling times and said calculation times, when said switching timearrives for switching between state V_(adj) to state V₀, sending saidSPmLL switch control signals to switch to said state V₀, j) if dt_(0r)≦T_(e), predicting the time of switching from said state V₀ to saidstate V'_(i) and identifying the new unique triplet (V'₀, V'_(i),V'_(adj)) for going from the predetermined position that is about to bereached to the next predetermined position of said stator flux vector,and k) asynchronously with said sampling times and said calculationtimes, when said switching time arrives to switch from state V₀ to stateV'_(i), sending said SPmLL switch control signals to switch to saidstate V'_(i), andprocessing the new unique triplet (V'₀, V'_(i),V'_(adj)) in accordance with steps c) through k) for respective valuesV'₀, V'_(i) and V'_(adj).
 13. The control process claimed in claim 12wherein in step c) said calculating step comprises solving the followingsystem to determine the remaining time dt_(ir) and updated timesdt_(adj) and dt₀ : ##EQU20## and in step f) said calculating stepcomprises solving the following system to determine the remaining timedt_(adjr) and the updated time dt₀ : ##EQU21## where λ is a parameterdefining the predictable final position of the current point B' on astraight line in said stator plane passing through said torque Γ axisand parallel to the predetermined position of said stator flux vector tobe reached.
 14. The process claimed in claim 12 wherein in step i)saidcalculating step comprises solving, for said current point C' (φ_(s)αc,φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application of said stateV₀ by solving the following system: ##EQU22## where Γ_(mean) is the meanelectromagnetic torque calculated over the time interval dt_(i)+dt.sub.αdj.
 15. The process claimed in claim 11 wherein the time dt₀ ofapplication of said null state is a decreasing function of said rotationspeed of said rotating machine and equal to zero beyond a predeterminedvalue of said rotation speed of said rotating machine.
 16. The processclaimed in claim 14 wherein if said time dt₀ of application of said nullstate is equal to zero the torque is controlled by a flux corrector as afunction of ΔΓ=Γ_(ref) -Γ_(c) in accordance with the following rules:forΔΓ>0 said corrector decreases the stator flux norm; for ΔΓ<0 saidcorrector increases the stator flux norm.
 17. A control system operableto variably control a rotating machine according to applicationconditions including n phases supplied with alternating current by avoltage inverter comprising n SPmLL switches, wherein m comprises anumber of levels represented by a single switch, said n SPmLL switchesdefining m^(n) states of a stator phase voltage vector, wherein anelectromagnetic torque Γ and a stator flux |φ_(s) | of said rotatingmachine are slaved to set points Γ_(ref), |φ_(s) |_(ref) by aservocontrol system that can employ various control strategies, eachstrategy having application conditions, said servocontrol systemincluding:a set of sensors; an observer-sampler receiving inputs fromthe set of sensors; a sampler receiving the outputs of said observer tosample the observer outputs at a given sampling time T_(e) to providesampled values; said calculating device receiving the sampled values andsaid calculating device outputting control signals for said SPmLLswitches of said voltage inverter, in accordance with said applicationconditions;wherein said calculating device calculates a succession of nstates of said phase voltage vector to move said torque Γ and said flux|φ_(s) | towards said set points Γ_(ref), |φ_(s) |_(ref) by successivelyswitching said n states of said succession and an application timedt_(k) where k ε{1, . . . n} for applying each of said n states of saidsuccession, wherein on each sampling, said calculating device calculatesa remaining application time of a current state and updated applicationtimes of future states of said phase vector, and asynchronously with thesampling times and the calculating times, at the end of the applicationtime of said current sate, said calculating device sends SPmLL switchcontrol signals to switch from said current state to the next state. 18.The control system claimed in claim 17, wherein said calculating deviceperforms calculations in an orthogonal three-dimensional calculationframe of reference comprising a stator plane (φ_(s)α, φ_(s)β) of saidstator flux φ_(s) and an axis perpendicular to said stator plane(φ_(s)α, φ_(s)β) representing said torque Γ, wherein said set pointsΓ_(ref) |φ_(s) |_(ref) are represented by a circle η_(ref) contained ina plane parallel to said stator plane (φ_(s)α, φ_(s)β), centered on saidperpendicular axis, having a radius |φ_(s) |_(ref) and intercepting saidperpendicular axis at Γ_(ref),wherein the values Γ, φ_(s) supplied bythe rotating machine are represented by a point A (φ_(s)α φ_(s)β, Γ) ona circle η contained in a plane parallel to said stator plane (φ_(s)α,φ_(s)β), centered on said perpendicular axis, having a radius |φ_(s) |and intercepting said perpendicular axis at Γ, and wherein saidcalculating device provides a control strategy which is asynchronouswith a rotation frequency of the rotating machine and wherein saidcalculating device calculates said succession of n states of saidvoltage vector such that said point A (φ_(s)α, φ_(s)β, Γ) converges toany point D of a circle η_(cal), centered on said perpendicular axis,having a radius |φ_(s) |_(cal) and intercepting said perpendicular axisat Γ_(cal) by successive application of said n states, in apredetermined given time; said calculating device further calculates theequation of said circle η_(cal) so that the application times of saidsuccession of phase vector voltages generates a mean torque Γ and a meanstator flux that are respectively substantially equal to said set pointsΓ_(ref), |φ_(s) |_(ref).
 19. The control system claimed in claim 18wherein, n being equal to three, said control strategy is based on acycle such that said calculating devices searches for a unique tripletof states (V₀, V_(i), V_(adj))iε{2. . . m^(n) -1} of said m^(n) possiblevoltage vector states, said unique triplet consisting a succession ofthree states comprising an initial state V_(i), one of the two statesV_(adj) adjacent to V_(i) and a null state (V₀), and wherein respectiveapplication times dt_(i), dt_(adj), dt₀ of said unique triplet arepositive and such that their sum is equal to half a switching periodT_(d) of said inverter.
 20. The control system claimed in claim 19wherein:a) said calculating device searches for the unique triplet andcalculates a presumed arrival point D' on said circle η_(cal), b) saidcalculating device sends said SPmLL switch control signals to switch tosaid state V_(i) based on said presumed arrival point, then c) on eachsampling, said calculating device calculates for a current point A'(φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining time dt_(ir) of application ofsaid state V_(i) and the updated times dt_(adj) and dt₀ of the futurestates V_(adj) and V₀, d) said calculating device determines whetherdt_(ir) ≦T_(e) and if so, said calculating device predicts the switchingtime from said state V_(i) to said state V_(adj), e) asynchronously withsaid sampling times and said calculation times, when said switching timearrives for switching from said state V_(i) to said state V_(adj), saidcalculating device sends said SPmLL switch control signals to switch tosaid state V_(adj), f) on each sampling, said calculating devicecalculates for a current point B' (φ_(s)αc, φ_(s)βc, Γ_(c)) a remainingtime dt_(adjr) of application of said state V_(adj) and an updated timedt₀ of said future state V₀, g) said calculating device determineswhether dt_(adjr) ≦T_(e) and if so, said calculating device predicts theswitching time from said state V_(adj) to said state V₀, then h)asynchronously with said sampling times and said calculation times, whensaid switching time arrives for switching from said state V.sub.αdj tosaid state V₀, said calculating device sends said SPmLL switch controlsignals to switch to said state V₀, then, i) on each sampling, saidcalculating device calculates for a current point C' (φ_(s)αc, φ_(s)βc,Γ_(c)) a remaining time dt_(0r) of application of said state V₀, j) saidcalculating device determines whether dt_(0r) ≦T_(e) and if so, saidcalculating device searches for a new unique triplet (V'₀, V'_(i),V'_(adj))iε{2. . . m^(n) -1} and predicts a switching time from saidstate V₀ to said state V'_(i), then k) asynchronously with said samplingtimes and said calculation times, when said switching time arrives forswitching from said state V₀ to said state V'_(i), said calculatingdevice sends said SPmLL control signals to switch to said state V'_(i),thensaid calculating device processes the new triplet (V'₀, V'_(i),V'_(adj)) according to features c) through k) on values V'₀, V'_(i),V'_(adj).
 21. The control system claimed in claim 20, wherein in item c)said calculating device solves the following system to determine theremaining time dt_(ir), and the updated times dt_(adhr) and the updatedtime dt₀ : ##EQU23## where λ is a parameter defining the position ofsaid point D on a tangent to said circle η_(cal) at D', where (1/2)T_(d)-t_(c) is a time remaining before a new period (1/2)T_(d) and in item f)said calculating device solves the following system using the leastsquares method to determine the remaining time dt_(adj) and the updatedtime dt₀ ; ##EQU24##
 22. The system claimed in claim 20, wherein in itemi) said calculating device calculates for said current point C'(φ_(s)αc, φ_(s)βc, Γ_(c)) the remaining time dt_(0r) of application ofsaid state V₀ by using a least squares method to solve the followingsystem: where (1/2)T_(d) -t_(c) is time remaining before a new period(1/2)T_(d).
 23. The system claimed in claim 20 wherein in saidcalculating device predicts the switching from said state V_(i) in orderto re-align the trajectory of said point B' towards said circle η_(cal).24. The system claimed in claim 20, wherein if said calculating devicefails to find a unique triplet (V₀, V_(i), V_(adj)) said calculatingdevice looks for a succession of two states (V_(i), V_(adj)) other thana null state for a best approximation to said point A (φ_(s)α, φ_(s)β,Γ) on said circle η_(ref) in the time interval (1/2)T_(d).
 25. Thecontrol system claimed in claim 17, wherein said calculator performscalculations in an orthogonal three-dimensional calculation frame ofreference comprising a stator plane (φ_(s)α, φ_(s)β) of said stator fluxφ_(s) and an axis perpendicular to said stator plane (φ_(s)α, φ_(s)β)representing said torque Γ, wherein said set points Γ_(ref), |φ_(s)|_(ref) are represented by a circle η_(ref) contained in a planeparallel to said stator plane (φ_(s)α, φ_(s)β), centered on saidperpendicular axis, having a radius |φ_(s) |_(ref) and intercepting saidperpendicular axis at Γ_(ref),wherein the values Γ, φ_(s) supplied bythe rotating machine are represented by a point A (φ_(s)α, φ_(s)β, Γ) ona circle η contained in a plane parallel to said stator plane (φ_(s)α,φ_(s)β), centered on said perpendicular axis, having a radius |φ_(s) |and intercepting said perpendicular axis at Γ, and wherein saidcalculating device provides a control strategy which is synchronous witha rotation frequency of the rotating machine and wherein saidcalculating device calculates a succession of n states of said voltagevector so that said point A (φ_(s)α, φ_(s)β, Γ) converges to a point Don a circle η_(cal) centered on said perpendicular axis, having a radius|φ_(s) |_(cal) and intercepting said perpendicular axis at Γ_(cal), bysuccessive application of said n states, with a predetermined finalposition of said stator flux vector in said stator plane (φ_(s)α,φ_(s)β); said calculating device further calculating the equation ofsaid circle η_(cal) so that the application times of said succession ofsaid phase vector voltage generates a mean torque Γ and a mean statorflux |φ_(s) | that are respectively substantially equal to said setpoints Γ_(ref), |φ_(s) |_(ref).
 26. The control system claimed in claim25 wherein a number of predetermined positions authorized for eachrotation of said stator flux is finite and dependent on a range ofrotation speed of the rotating machine.
 27. The control system claimedin claim 25 wherein n is equal to three, and said control strategy issuch that said calculating device sets a unique triplet of states (V₀,V_(i), V_(adj)) iε{2. . . m^(n) -1} of said voltage vector constitutinga succession of three states, comprising an initial state V_(i), one ofthe two states V_(adj) adjacent to V_(i) and a null state (V₀), therespective application times dt_(i), dt_(adj), dt₀ of which arenegative, said triplet intercepting said circle η_(cal) at a known pointD.
 28. The control system of claim 27 further including a memorywherein, triplets (V₀, V_(i), V_(adj))iε{2. . . m^(n) -1} are stored insaid memory and in operation,a) said calculating device sets the triplet(V₀, V_(i), V.sub.αdj) to be applied according to the rotation speed ofsaid rotating machine and the predetermined position at which saidstator flux vector is located, b) said calculating device sends saidSPmLL switch control signals to switch to state V_(i), c) on eachsampling, said calculating device calculates for a current point A'(φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining time dt_(ir) of application ofsaid state V_(i) and updated times dt_(adj) and dt₀ of said futurestates V_(adj) and V₀, d) said calculating device determines whetherdt_(ir) ≦T_(e) and if so, said calculating device predicts the time ofswitching from said state V_(i) to state V_(adj), e) asynchronously withsaid sampling times and said calculation times, when said switching timearrives to switch from said state V_(i) to said state V_(adj), saidcalculating device sends said SPmLL switch control signals to switch tostate V_(adj), f) on each sampling, calculating device calculates for acurrent point B' (φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining time dt_(adjr) ofapplication of said state V.sub.αdj and an updated time dt₀ of saidfuture state V₀, g) said calculating device determines whether dt_(adjr)≦T_(e), and if so, said calculating device predicts the time ofswitching from said state V_(adj) to said state V₀, h) asynchronouslywith said sampling times and said calculation times, when said switchingtime arrives to switch from said state V_(adj) to state V₀, saidcalculating device sends said SPmLL switch control signals to switch tosaid state V₀, i) on each sampling said calculating device calculatesfor a current point C' (φ_(s)αc, φ_(s)βc, Γ_(c)) a remaining timedt_(0r) of application of said state V₀, j) said calculating devicedetermines whether dt_(0r) ≦T_(e), and if so, said calculating devicepredicts the time of switching from said state V₀ to said state V'_(i)and additionally said calculating device sets a new unique triplet (V'₀,V'_(i), V'_(adj)) for going from the predetermined position that isabout to be reached to the next predetermined position of said statorflux vector, and k) asynchronously with said sampling times and saidcalculation times, when said switching time arrives for switching fromstate V₀ to state V'_(i), said calculating device sends said SPmLLcontrol signals to switch to said state V'_(i),said calculating deviceprocessing the new unique triplet (V'₀, V'_(i), V'_(adj)) in accordancewith features c) through k) for V'₀, V'_(i), V'_(adj).
 29. The controlsystem claimed in claim 28 wherein in item c) said calculating devicesolves the following system to determine the remaining time dt_(ir) andthe updated times dt_(dj) and dt₀ : ##EQU25## and in item f) saidcalculating device solves the following system to determine theremaining time dt_(adj) and the updated time dt₀ : ##EQU26## where λ isa parameter defining the predictable final position of the current pointB' on a straight line in said stator plane passing through said torque Γaxis and parallel to the predetermined position of said stator fluxvector to be reached.
 30. The system claimed in claim 28 wherein in itemi)said calculating device calculates for said current point C' (φ_(s)αc,φ_(s)β c, Γ.sub.) the remaining time dt_(0r) of application of saidstate V₀ by solving the following system: ##EQU27## where Γ_(mean) isthe mean electromagnetic torque calculated over the time interval dt_(i)+dt_(adj).
 31. The system claimed in claim 27 wherein the time dt₀ ofapplication of said null state is a decreasing function of said rotationspeed of said rotating machine and equal to zero beyond a predeterminedvalue of said rotation speed of said rotating machine.
 32. The systemclaimed in claim 31 wherein if said time dt₀ of application of said nullstate is equal to zero the torque is controlled by a flux corrector as afunction of ΔΓ=Γ_(ref) -Γ_(c) in accordance with the following rules:forΔΓ>0 said corrector decreases the stator flux norm; for ΔΓ<0 saidcorrector increases the stator flux norm.
 33. The system of claim 18including a rotating machine providing inputs to said set of sensors andconnected to said SPmLL switches, wherein said rotating machine has atorque and stator flux adjusted according to the control signalscalculated by the calculating device.
 34. The system of claim 20including a rotating machine providing inputs to said set of sensors andconnected to said SPmLL switches, wherein said rotating machine has atorque and stator flux adjusted according to the control signalscalculated by the calculating device.
 35. The system of claim 25including a rotating machine providing inputs to said set of sensors andconnected to said SPmLL switches, wherein said rotating machine has atorque and stator flux adjusted according to the control signalscalculated by the calculating device.
 36. The system of claim 28including a rotating machine providing inputs to said set of sensors andconnected to said SPmLL switches, wherein said rotating machine has atorque and stator flux adjusted according to the control signalscalculated by the calculating device.